Process of producing non-fibrillating acrylonitrile polymer filaments



United States Patent C) 3 129 273 PROCESS (NF PRUDUIHNG NON-FEBRILLATHNGCRYLNiT-RLE PGLYMER FILAMENTS Fred .'i. Lowes, Jr., Midiand, Mich.,assigner to The Dow Chemical Company, Midiand, Mich., a corporation ofDelaware Filled Dec. lll, 196i, Ser. No. 158,593 5 Claims. (Ci. 264-182)This invention relates to a process for preparing improved acrylonitrilepolymer structures. It relates more particularly to the preparation ofnon-fibrillating acrylonitrile polymer structures prepared by treatingsaid structures (while in the aquagel form) with certain substantiallywater-insoluble polyoxyalkylene glycols.

By structures as employed throughout the instant specification andclaims, is meant fibers, filaments, bundles of filaments, yarns,threads, foils, ribbons, films, and the like. However, for the sake ofsimplicity of description, the present invention will be described as itis applicable to the production of filaments, including bundles offilaments and fibers, it being understood that this is merely intendedin an illustrative sense and the invention should not be limitedthereby, but only insofar as the same may be limited by the appendedclaims.

Polyacrylonitrile and many of the fiber and film-forming copolymers ofacrylonitrile may advantageously be fabricated by a wet spinning processwherein the polymer composition is extruded from compositions of thepolymer in polyacrylonitrile-dissolving aqueous saline solvents,particularly aqueous solutions of zinc chloride and its salineequivalents. Such a procedure, as is well known in the art, isoftentimes referred to as salt-spinning with the fibers (or other shapedarticles) obtained thereby being salt-spun. In salt-spinning, thefiber-forming, aqueous saline spinning solution or other composition ofthe polymer is extruded during the spinning operation into anon-polymer-dissolving coagulation liquid, or spin bath, whichfrequently is a solution of the same salt or salts as are in thespinning solution.

Acrylonitrile polymers (including fiber-forming copolymers),particularly polyacrylonitrile, that are saltspun in the referred-tomanner are generally formed as aquagel intermediates. Such intermediateshave a waterswollen or hydrated structure prior to their being finallyirreversibly dried to the desired, characteristically hydrophobic,product.

Advantageously, the aquagel structures of polyacrylonitrile and otherfiberand film-forming acrylonitrile polymers may be derived by theextrusion into and coagulation in an aqueous coagulating spin bath of asolution of the acrylonitrile polymer that is dissolved in an aqueouszinc chloride saline solvent therefor. It is usually desirable for zincchloride to be at least the principal (if not the entire) saline solutein the aqueous saline solvent solution.

lf preferred, however, various of the saline equivalents for zincchloride may also be employed in the aqueous saline solvent medium forthe spinning solution and the coagulating bath utilized. Those zincchloride equivalents, as is Well known, include various of thethiocyanates (such as calcium thiocyanate), lithium bromide and thesalts and salt mixtures that are solvent members of the so-calledlyotropic series as are disclosed among other places in U.S. 2,140,921;2,425,192; 2,648,592; 2,648,593; 2,648,646; 2,648,648; and 2,648,649.

Filaments produced from acrylonitrile polymers by the wet spinningprocess have excellent physical properties but do suffer from oneserious defect, namely, fibrillation.

The term fibrillation is used in the textile industry 3,129,273 PatentedApr. 14, 1964 to indicate a type of fiber disintegration or longitudinalfracture generally along the lines of molecular orientation. As aconsequence of fibrillation the fiber or filament is longitudinallydivided into segments or fibrils. Often, fibrillation may result in afrosty or whitened appearance, even of dyed fibers and fabrics.

The loss of color or change toward White is affected by severalvariables including the amount of division and size of fibrils producedduring processing of the spun product. Fibrils can be of such smalldiameter that incident light is scattered. Fibrillation of textilefibers and fabric produced therefrom appears to result from transverseforces which ultimately cause a shattering of the fiber along the linesof least resistance, namely, longitudinally. Thus, a fiber or relatedfilamentous article having greater characteristic fiexibility may oftenbe less prone to fibrillation than a corresponding relatively Vlessflexible article.

Accordingly, it is the primary object of the present invention toprovide a method of preparing substantially non-fibrillating textilefibers or like filamentous structures from high acrylonitrile polymers(i.e., those containing at least weight percent of polymerizedacrylonitrile in the polymer molecule).

Other and related objects will become evident from the followingspecification and claims.

In accordance with the present invention, substantially non-fibrillatingsynthetic polymer textile filaments are prepared by salt spinningacrylonitrile polymers (which polymer contains in the polymer moleculeat least about 85 weight percent of acrylonitrile, any balance beinganother monoethylenically unsaturated monomeric material that iscopolymerizable with acrylonitrile), into an aquagel filamentarystructure that contains between about l and 5 parts by weight of waterto each part by weight of dry polymer therein; washing said aquagelstructure substantially free from residual salt, and physicallyelongating the filament aquagel by stretching said aquagel to an atleast partially oriented condition; subjecting said aquagel to intimatecontact with a homogeneous aqueous emulsion containing at least about 1weight percent based on the weight of the emulsion, of a substantiallywaterinsoluble polyoxyalkylene glycol (as will be described);maintaining said aquagel in Contact with the emulsion at a temperaturebetween about 60 C. and 100 C. for a period of between about 2 minutesto 4 hours; and subsequently irreversibly drying the aquagel filament toa synthetic characteristically hydrophobic textile fiber structure.

In the annexed drawing there is shown a flow sheet in accordance withthe herein claimed process.

The acrylonitrile polymer employed in practice of the present inventionis, advantageously, polyacrylonitrile, although, as is readily apparent,any of the well-known ber and film-forming copolymers thereof thatcontain, polymerized in the polymer molecule, at least 85 weight percentof acrylonitrile with at least one other ethylenically unsaturatedmonomer that is copolymerizable with acrylonitrile may, beneficially,'be utilized. The acrylonitrile polymer employed is soluble in anaqueous saline solvent for acrylonitrile which, usually, has therein atleast about 50-60 weight percent of zinc chloride or its salineequivalents. U.S. 2,776,946, among many other reference sources, setsforth many of the monomers which may be Ycopolyrnerized orinterpolymerized with acrylonitrile to produce binary or ternaryacrylonitrile copolymers that are useful in the practice of thisinvention.

Specific polyoxyalkylene glycols that are suitable for instant purposesinclude, but are not restricted to, polyoxypropylene glycols having anaverage molecular weight of about 2000; polyoxybutylene glycols havingan average molecular weight of about 2000; and suitably mixedpolyoxyalkylene glycols wherein the polymer chains contain two or moredifferent oxyalkylene units, either as a random sequence (heteric) or assegregated blocks (block copolymers). Ordinarily, water-insolubleglycols having average molecular weights between about 1000 and 3000 aresuitable.

The polyoxyalkylene glycols suitably used in the present invention mustbe present in the aqueous emulsion in a minimum amount of about 1 weightpercent based on the weight of the emulsion. The permissible maximumproportion depends on the particular polyoxyalkylene glycol beingemployed; the ability of the glycol to form a stable homogeneousemulsion with water; and the compatibility of the glycol with theacrylonitrile polymer aquagel. The maximum limit is generally about 20weight percent, based on the Weight of the emulsion. Glycolconcentrations greater than about 20 weight percent based on emulsionweight oftentimes form two phase systems with water and are not usefulfor the present invention.

The amount of polyoxyalkylene glycol present in filaments produced fromsalt-spun acrylonitrile polymers is dependent upon, and approximately inthe same ratio as, the amounts of said glycols present in the aqueousemuls1on.

It has been observed that only the glycols as defined herein aresuitable for achieving the ends of the present invention. p

For example, polyoxyalkylene glycols of the type here described buthaving a viscosity at 100 F. less than about 100 centistokes are notsufiiciently insoluble in water to provide the ends of the presentinvention.

Additionally, polyoxyalkylene glycols of the type here described havinga molecular weight greater than about 3000 or a viscosity at 100 F. ofgreater than about 260 centistokes have limited compatibility with theacrylonitrile polymer aquagel and, as a consequence, are not useful forthe present invention.

The preparation of the polyoxyalkylene glycols useful in practice of thepresent invention is well known to those skilled in the art. U.S.2,056,830 describes a method of preparing polyglycols by partialdehydration of the corresponding simple glycols in the presence ofdehydration catalysts. By a dehydration catalyst is meant a substancewhich is capable of prompting splitting of water from a simple glycol,e.g., propylene glycol, with intramolecular formation of glycol etherswhen such simple glycol is heated in its presence.

The desirable properties of synthetic textile fibers and likefilamentous articles produced by the methods of the present inventionare derived by incorporation of the suitable polyoxyalkylene glycolsdescribed herein, into the acrylonitrile polymer aquagel structure.

As previously noted, the aquagel structure is generally stretched to anat least partially oriented condition prior to immersing said aquagelvstructure in the aqueous polyoxyalkylene glycol emulsions describedherein. Orientation of the aquagel structure is accomplished to increasethe tenacity of the filament of said aquagel structure to a practicalpoint.

It has been observed that non-oriented acrylonitrile polymer aquagelstructures which have been treated with the 'aqueous polyoxyalkyleneglycol emulsions, as described herein, and subsequently oriented in theindicated manner, form synthetic textile fibers and like filamentousarticles having similar desirable properties.

The acrylonitrile'polymer aquagels must be immersed in Vthe aqueouspolyoxyalkylene glycol emulsions described herein, for periods ofbetween about 2 minutes and 4 hours, preferably from about 5 to 10minutes, at a 'temperature ranging between about 60 C. and 100 C.,

to obtain the ends of the present invention.

Temperatures less than about 60 C. are not sufiicient to provide thedesirable results described herein, and immersion periods greater thanabout 4 hours may at least partially hydrolyze the polyoxyalkyleneglycol constituent of the homogeneous emulsion.

The following example, wherein all parts and percentages are to be takenby weight, illustrates the present invention but is not to be construedas limiting its scope.

Example 1 In each of a series of experiments, a charge of about 35 gramsof a solution consisting of =10 percent polyacrylonitrile, 54 percentzinc chloride, and 36 percent water, all based on the total weight ofthe solution, was placed in a bottle.

The spinning solution was extruded through a spinnerette having about300 individual orifices (each orifice having a diameter of about 3mils), into an aqueous nonpolymer-dissolving zinc chloride coagulatingbath.

The aquagel formed therein was spun into a multiple lament tow andcollected on a magnesium bar covered with aluminum foil. The resultingaquagel filament tow was then water washed until substantially free ofzinc chloride.

There was thereby obtained an aquagel filament tow containing about lpart water for each part of acrylonitrile polymer therein. The aquagelfilament tow was oriented by being stretched to a length of about 10 tol2 times its original extruded length.

The oriented tow was then cut in individual shorter' lengths and severalof the individual shorter lengths individually boiled for a period ofabout 5 minutes in a homogenized aqueous emulsion containing about 5weight percent based on emulsion weight, of a substantiallywaterinsoluble polyoxypropylene glycol having an average molecularweight of about 2000 and a viscosity at 100 F. of about 164 centistokes.

Each of the resulting brous materials were dried: combed out fiat; andcemented at each end of a glass slide. Each of the glass slides werefastened to the pan of a Welsh triple-beam laboratory balance. The Welshbalance was mounted on a milling vice by means of which, each fibersample was traversed under a vibrating ball in a test of fibrillationresistance.

In each of the tests five passes of the tool were made at right anglesto the fiber axis (about ls inch apart), under loads of 1, 4, 16, 64,and 128 grams, respectively. Rating of fibrillation resistance was byvisual and microscopic inspection.

Fibers which gave no perceptible fibrillation at 64 grams or more wererated excellent. Those which fibrillated noticeably at 16 grams or lesswere rated fair to poor.

Each of the polyacrylonitrile fibrous materials treated with the aqueouspolyoxyalkylene glycol emulsions as described herein, fibrillated onlyslightly under loads of 64 to 128 grams and, consequently, had afibrillation rating of excellent.

Equivalent, but untreated polyacrylonitrile fibrous materialsfibrillated noticeably under a load of 16 grams and, consequently, wereassigned a fibrillation rating of fair to poor.

Similar desirable resistance to fibrillation is obtained using anyconcentration between about l and 20 weight percent based on emulsionweight of the polyoxypropylene glycol described herein.

In like manner similar desirable resistance to fibrillation is obtainedusing any concentration between about 1 and 20 weight percent based onemulsion weight of a polyoxybutylene glycol having an average molecularweight of about 2000 and a viscosity at 100 F. of about 258 centistokes(such glycol being a viscous liquid which is less than about 0.1 percentsoluble in water at 25 C.).

On the other hand, polyoxypropylene glycols having a viscosity at 100 F.of less than about 100 centistokes, and polyoxyethylene glycols having amolecular weight ranging from about 200 to 2000, and correspondingviscosities at 100 F. of more than about 20 centistokes to that of asolid material, are insuciently insoluble in water and are not usefulfor the present invention.

Polyoxypropylene glycols that have an average molecular weight greaterthan about 3000 and a corresponding viscosity at 100 F. greater thanabout 260 centistokes are insuiiciently compatible with mostacrylonitrile polymers of interest to be useful for the presentinvention.

Similar good results, as noted above in Example 1 carried out inaccordance with this invention, are obtained when berand hlm-formingacrylonitrile polymers containing at least 85 weight percent ofpolymerized acrylonitrile and up to weight percent of one or more ofsuch copolymerizable materials as vinyl chloride, vinyl acetate, methyland other alkyl acrylates or methacrylates, the vinyl pyridines, allylalcohol, and many others Well known to those skilled in the art areadmixed with the polyoxyalkylene glycols suitable for use in practice ofthe present invention.

What is claimed is:

1. Method of preparing a non-brillating synthetic acrylonitrile polymertextile liber which method comprises:

(a) salt spinning a liber-forming acrylonitrile polymer, which polymercontains in the polymer molecule at least about 85 weight percent ofacrylonitrile, any balance being another monoethylenically unsaturatedmonomeric material that is copolymerizable with acrylonitrile, into anaquagel lamentary structure that contains between about 1 and 5 parts byweight of water to each part by weight of dry polymer therein;

(b) washing said aquagel structure substantially free from residualsalt;

(c) physically elongating said aquagel structure by stretching it to anat least partially oriented condition;

(d) subjecting for from 2 minutes to about 4 hours the so-formed aquagelfiber to intimate contact with a homogeneous aqueous emulsion containingat least 1 weight percent of a substantially water-insolublepolyoxyalkylene glycol having an average molecular weight between about1000 and 3000 and a viscosity at 100 F. between about 100 and 260centistokes, said emulsion maintained at a temperature between about C.and 100 C.; and

(e) subsequently irreversibly drying said aquagel ber to a syntheticcharacteristically hydrophobic textile iiber structure.

2. The method of claim l, wherein the substantially Water-insolublepolyoxyalkylene glycol is present in amounts between about 1 and 20weight percent, based on the weight of the homogeneous emulsion.

3. The method of claim 1, wherein said polyoxyalkylene glycol ispolyoxypropylene glycol with an average molecular weight of about 2000and a viscosity at F. of about 164 centistokes.

4. The method of claim 1, wherein said polyoxyalkylene glycol ispolyoxybutylene glycol with an average molecular weight of about 2000and a viscosity at 100 F. of about 258 centistokes.

5. The method of claim l, wherein said acrylonitrile polymer ispolyacrylonitrile.

Textile Chemicals and Auxiliaries, 2nd ed., by Speel et al., publishedby Reinhold Publishing Corp., 1957, Scientific Library, call No. TS 1449S 64; p. 286 is relied upon.

1. METHOD OF PREPARING A NON-FIBRILLATING SYNTHETIC ACRYLONITRILEPOLYMER TEXTILE FIBER WHICH METHOD COMPRISES: (A) SALT SPINNING AFIBER-FORMING ACRYLONITRILE POLYMER, WHICH POLYMER CONTAINS IN THEPOLYMER MOLECULE AT LEAST ABOUT 85 WEIGHT PERCENT OF ACRYLONITRILE, ANYBALANCE BEING ANOTHER MONOETHYLENICALLY UNSATURATED MONOMERIC MATERIALTHAT IS COPOLYMERIZABLE WITH ACRYLONITRILE, INTO AN AQUAGEL FILAMENTARYSTRUCTURE THAT CONTAINS BETWEEN ABOUT 1 AND 5 PARTS BY WEIGHT OF WATERTO EACH PART BY WEIGHT OF DRY POLYMER THEREIN; (B) WASHING SAID AQUAGELSTRUCTURE SUBSTANTIALLY FREE FROM RESIDUAL SALT; (C) PHYSICALLYELONGATING SAID AQUAGEL STRUCTURE BY STRETCHING IT TO AN AT LEASTPARTIALLY ORIENTED CONDITION; (D) SUBJECTING FOR FROM 2 MINUTES TO ABOUT4 HOURS THE SO-FORMED AQUAGEL FIBER TO INTIMATE CONTACT WITH AHOMOGENEOUS AQUEOUS EMULSION CONTAINING AT LEAST 1 WEIGHT PERCENT OF ASUBSTANTIALLY WATER-INSOLUBLE POLYOXYALKYLENE GLYCOL HAVING AN AVERAGEMOLECULAR WEIGHT BETWEEN ABOUT 1000 AND 3000 AND A VISCOSITY AT 100*F.BETWEEN ABOUT 100 AND 260 CENTISTOKES, SAID EMULSION MAINTAINED AT ATEMPERATURE BETWEEN ABOUT 60*C. AND 100*C.; AND (E) SUBSEQUENTLYIRREVERSIBLY DRYING SAID AQUAGEL FIBER TO A SYNTHETIC CHARACTERISTICALLYHYDROPHOBIC TEXTILE FIBER STRUCTURE.